Sōhaku is the first and only person to ever be head of the Kago family, as he has lived for several centuries because of his unique power. He also is the true head of F. For unknown reasons, it has been his goal to awaken dormant powers in people across the world through the use of the Red Wing Resonance Effect. At one time he had a relationship with Makiko Nagi, and fathered Souchiro as a result.
He typically appears with white slicked back hair, a young face and narrow eyes (sometimes with goggles on his head).
He will get what he wants by any means even seemingly brainwashing and possessing people through the use of various jutsus, and he has a habit of getting rid of people when they are no longer useful to him. He has always been in conflict with the other founding families and is often responsible for many of their deaths.
Much like Dōgen Takayanagi, Sohaku has some desire to make an ultimate warrior. He uses a different means than Dogen, as he views the ultimate warrior as someone that could use all the dragon’s gates. He attempted to do this with Makiko by using of her family’s ability, the Dragon's Fist, to absorb the other families’ powers. However, he deemed it a failure as he concluded that Makiko’s body was too weak to handle her dragon. He did repeat the same process eight years later with his son, Souichiro, and achieved better results.
Sohaku has apparently survived without most people figuring out he is nearly immortal by frequently assuming new personas. In Feudal Japan, Sohaku initially went by the name Akechi Mitsuhide, who is a real person in Japanese history. Much like the historical Akechi was suspected of doing, he faked his death and then claimed to be a High Buddhist priest named Tenkai. Like the historical Tenkai, he supposedly functioned as an advisor to Ieyasu Tokugawa. However, in the manga's version of history, he essentially controlled the local government through a magical jutsu he used on a then isolated Ieyasu.
Sōhaku was never animated as the anime and OVA's didn't get that far into the storyline. He appears solely in the manga and seems to play the role of the primary antagonist in the story.
Sōhaku first appears when he kidnaps Souichiro from the hospital and forces him to fight various people with Red Feather Powers so he can steal their powers. Mitsuomi and Maya work together to rescue Souichiro and kill Sōhaku. Despite the fact Souichiro and Madoka Mawari are hesitant to kill Sōhaku, Mitsuomi quickly beheads him. Mitsuomi then leaves to assist Maya in her recovery after her battle with Tetsuhito, and sends Madoka away with Reiki to assist Tessen Ishiyumi and the others. Souichiro remains in the room alone were he is confronted with Noriko, who has the power to control others through use of her Dragon Roar. During this time, Reiki manifests itself for Aya Natsume in order to guide her to view certain points in past for Aya to understand Sōhaku better. It initially shows her the origins of Tetsuhito's powers, and Makiko's relationship with Sōhaku
Later Reiki takes Aya to another point in history, it is during the Feudal Japan Era. At this time Aya’s ancestor is with group of various red feather family members trying to kill Sōhaku in order to bring peace. Sōhaku had fortified himself inside Osaka Castle with Senhime, the Magatama Shrine Maiden, whose power caused the neutralization of other’s power when in close proximity. Since Sōhaku knew the other families were coming after him, he built a barrier that would reverse the Magatama Shrine Maiden’s power and turn it into amplification. When the Red Feathers attacked him, their power would cause a Resonance Effect that would go around the world awake all the dormant power users. His plan failed when Masanobu Sadonokami Honda helped Aya’s ancestor to sneak into the castle, so she could stab him. He was fatally wounded and could not use his power because he was in the same room as the Magatama Shrine Maiden. After he killed his attacker, he transferred his consciousness in his right eye and somehow hid it inside Senhime’s dead dog. There he waited until Senhime was removed from the Castle and he could use his power to resurrect the dog and leave. Two years later, Tetsuhito and Noriko attack Tokuan Shōjō, Masanobu, and Ieyasu Tokugawa. Impersonating the believed to be dead Sōhaku, Tokuan Shōjō gets his eye ripped out and replaced by Sōhaku’s. This allowed him to gain full control over the body and is also the reason why he still looks like himself. Afterward he forces the other families to call a truce by promising that he will not cause more trouble for a little while.
Back in the present time Noriko, carrying Sōhaku's severed head, takes out Souichiro's right eye and it is implied Sōhaku's is inserted in its place. Unlike before, Sōhaku does not take complete control over the body, but instead seem content waiting for the right time.
As Aya has her confrontation with Hirohiko Myouun Kabane and Nokimi Mayutsubo, it is implied that in his next fight against someone with special powers Souichiro will be overtaken by his dragon. This is part of Sohaku's plan as he wishes to overtake Souichiro at that time.
Sohaku seems to also want to create another barrier that will activate Maya's Amaterasu Dragon's Gate. However, this barrier, in contrast with the one he created in Feudal Japan, actually encompasses all of Japan itself.